CN116114259A

CN116114259A - PWM driver, method of generating PWM signal, actuator system, and camera module

Info

Publication number: CN116114259A
Application number: CN202080105139.6A
Authority: CN
Inventors: 石井隆雄
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2023-05-12
Also published as: WO2022021202A1

Abstract

A PWM driver is provided that can reduce noise on a camera module caused by PWM controlled OIS/AF actuators. The PWM driver for generating a PWM signal for driving a lens includes: a PWM signal generator for generating a reference PWM signal switched at a predetermined period; a receiving unit configured to receive a mask signal defining a switching prohibition period; a modulation unit for generating an actual PWM signal by not switching the reference PWM signal during the switching prohibition period defined by the mask signal.

Description

PWM driver, method of generating PWM signal, actuator system, and camera module

Technical Field

The present invention relates to a PWM driver, a method for generating a PWM signal, an actuator system and a camera module, and more particularly, to a PWM driver for generating a PWM signal for driving a lens, a method for generating a PWM signal, an actuator system and a camera module.

Background

Electronic devices such as smartphones and miniature cameras include an optical image stabilization (optical image stabilization, OIS)/auto-focus (AF) actuator for externally controlling the camera unit. For example, SMA wires are known for use as actuators. In this case, the SMA wire is used for OIS driving of an optical image of the camera by driving tilting of a camera unit comprising a lens element of the camera and an image sensor. In this case, the OIS/AF actuator of the electronic apparatus outputs a signal modulated by a pulse width modulation (pulse width modulation, PWM) signal (hereinafter referred to as "PWM signal"). The PWM signal is a signal that switches between a high (H) state and a low (L) state at a predetermined period. In the actuator, the SMA wire is driven by the PWM signal to move the lens element in a desired direction.

PWM technology is a good candidate for a control method of driving OIS/AF actuators because it can reduce the power consumption of the camera module. However, repetition of H and L levels of the PWM signal output from the PWM driver may increase electrical noise and magnetic noise. Since the OIS/AF actuator is implemented close to the image sensor for moving the lens unit, noise of the PWM driver may affect the image signal.

Disclosure of Invention

The present invention provides a method of mitigating noise on a camera module caused by a PWM controlled OIS/AF actuator.

According to a first aspect, a PWM driver for generating a PWM signal for driving a lens, comprises:

a PWM signal generator for generating a reference PWM signal switched at a predetermined period;

a receiving unit configured to receive a mask signal defining a switching prohibition period;

a modulation unit for generating an actual PWM signal by not switching the reference PWM signal during the switching prohibition period defined by the mask signal.

According to this implementation, the actual PWM signal is generated by not switching the reference PWM signal during the switching prohibition period. Therefore, the influence of noise on the pixel output AD conversion can be eliminated without being limited by the combination of the PWM carrier frequency and the AD conversion period.

With respect to one possible implementation of the first aspect, the PWM signal generator generates the reference PWM signal based on a movement of the lens.

According to this implementation, the PWM signal may be generated taking into account the movement of the lens, such as the acceleration, speed and position of the lens.

With respect to one possible implementation of the first aspect, the generator obtains movement information from a gyroscopic sensor that detects the movement of the lens.

According to this implementation, the PWM signal generator may generate the reference PWM signal based on movement information in a gyro sensor that detects the movement of the lens.

With respect to a possible implementation manner of the first aspect, the switching prohibition period is set based on a control signal for performing analog-to-digital conversion of an image captured by the image sensor.

According to this implementation, the output level of the actual PWM signal can be maintained during one cycle of the AD conversion operation.

With reference to one possible implementation manner of the first aspect, the PWM driver further includes a counter for increasing or decreasing a counter value of a pulse number of a clock according to an H state or an L state of the actual PWM signal, wherein the modulation unit is configured to switch the actual PWM signal based on the counter value to minimize an absolute value of the counter value outside the switching prohibition period.

According to this implementation, the count number indicates a different duration of the output H/L state period than the H/L state period of the reference PWM signal. The actual PWM signal may be switched in consideration of the measurement result.

With respect to one possible implementation of the first aspect, the range of the counter corresponds to a period of the reference signal of the analog-to-digital conversion.

According to this implementation, overflow of the counter can be suppressed.

With respect to one possible implementation of the first aspect, the modulation unit switches the actual PWM signal when the counter value overflows during the switching prohibition period.

According to this implementation, PWM control can be continued with less noise while reducing the influence of counter overflow.

With respect to a possible implementation manner of the first aspect, the mask signal is generated based on a control signal for performing analog-to-digital conversion on an image captured by the image sensor.

According to this implementation, the switching prohibition period may be set by the mask signal so that the PWM state does not change in one period of the CDS, and noise caused by PWM state change in AD conversion of the image sensor is suppressed.

With respect to one possible implementation of the first aspect, the switching prohibition period is set such that the actual PWM signal is not switched during a conversion process of converting an analog signal of an image captured by the image sensor into a digital output.

According to this implementation, the switching prohibition period may be set so that the PWM state does not change in one period of the CDS.

With respect to a possible implementation manner of the first aspect, the PWM driver further comprises a monitor for instructing the modulation unit to switch the actual PWM signal based on the reference PWM signal and the actual PWM signal.

According to this implementation, the modulation unit may generate the actual PWM signal based on the output of the duty cycle error monitor and the reference PWM signal.

With respect to one possible implementation of the first aspect, the monitor instructs the modulation unit to switch the actual PWM signal such that the actual PWM signal approximates the duty cycle of the reference PWM signal.

According to this implementation, the average duty cycle may be the same as the duty cycle of the reference PWM signal.

With respect to a possible implementation manner of the first aspect, the PWM driver further includes a mask generating unit for generating the mask signal.

According to this implementation, the mask generating unit may be implemented in a PWM driver.

According to a second aspect, there is provided an actuator system comprising:

a PWM driver according to any implementation of the first aspect;

and a lens unit for driving the lens based on the actual PWM signal generated by the actual PWM driver.

According to a third aspect, there is provided a camera module,

the actuator system according to the second aspect;

an imaging unit for capturing an image using a lens driven by the actuator system.

According to a fourth aspect, there is provided a method for generating a PWM signal for driving a lens, comprising:

generating a reference PWM signal switched at a predetermined period;

receiving a mask signal defining a switching prohibition period;

an actual PWM signal is generated by not switching the reference PWM signal during the switching prohibition period defined by the mask signal.

With respect to a possible implementation manner of the fourth aspect, the step of generating the reference PWM signal generates the reference PWM signal based on a movement of the lens.

With respect to a possible implementation manner of the fourth aspect, the step of generating the reference PWM signal obtains movement information from a gyro sensor that detects movement of the lens.

With respect to a possible implementation manner of the fourth aspect, the switching prohibition period is set based on a control signal for performing analog-to-digital conversion on an image captured by the image sensor.

With respect to a possible implementation manner of the fourth aspect, the method further includes:

and increasing or decreasing a counter value of a pulse number of a clock according to an H state or an L state of the actual PWM signal, wherein the step of generating the reference PWM signal is based on the counter value to minimize an absolute value of the counter value outside the switching prohibition period.

With respect to one possible implementation manner of the fourth aspect, the range of the counter corresponds to a period of the reference signal of the analog-to-digital conversion.

With respect to one possible implementation manner of the fourth aspect, the step of generating the actual PWM signal switches the actual PWM signal when the counter value overflows during the switching prohibition period.

With respect to a possible implementation manner of the fourth aspect, the mask signal is generated based on a control signal for performing analog-to-digital conversion on an image captured by the image sensor.

With respect to one possible implementation of the fourth aspect, the switching prohibition period is set such that the actual PWM signal is not switched during a conversion process of converting an analog signal of an image captured by the image sensor into a digital output.

With respect to a possible implementation manner of the fourth aspect, the step of generating the actual PWM signal includes switching the actual PWM signal based on the reference PWM signal and the actual PWM signal.

With respect to a possible implementation manner of the fourth aspect, the step of generating the actual PWM signal switches the actual PWM signal such that the actual PWM signal approximates the duty cycle of the reference PWM signal.

With respect to a possible implementation manner of the fourth aspect, the method further includes the step of generating the mask signal.

Drawings

In order to more clearly describe the technical solutions in the embodiments, the drawings required for describing the present embodiments are briefly described below. It is evident that the figures in the following description depict only some of the possible embodiments, and that those skilled in the art may still obtain additional figures from these figures without inventive effort, in which:

fig. 1 shows a schematic diagram of the electrical connection of SMA-OIS.

Fig. 2 shows a configuration of time-division driving.

Fig. 3 shows the time variation of the PWM signal for driving the SMA wire.

Fig. 4 shows a bode plot of correlated double sampling (correlated double sampling, CDS) as a filter.

Fig. 5 shows a configuration of a CMOS image sensor in which column ADCs of pixel columns perform CDS.

Fig. 6 shows a signal diagram in CDS implemented on a COMS image sensor.

Fig. 7 shows a configuration example of the lens actuator system.

Fig. 8 shows a schematic diagram of signals for performing CDS in an ADC and PWM signals for OIS driving.

Fig. 9 illustrates a block diagram of a lens actuator system with a waveform modulator provided by one embodiment.

Fig. 10 shows a waveform diagram for explaining the waveform operation of the waveform modulator.

Fig. 11 shows a relationship between a RAMP signal and an act_pwm signal for AD conversion.

Fig. 12 illustrates a state transition diagram provided by one embodiment.

Fig. 13 shows a schematic diagram of the operating waveforms in the event of a duty cycle error monitor overflow.

Fig. 14 illustrates a state transition diagram provided by one embodiment.

Fig. 15 shows a block diagram of a lens actuator system with a waveform modulator.

Fig. 16 shows a signal diagram of a lens actuator system provided by an embodiment.

Detailed Description

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following description will make clear and complete descriptions of the technical solutions of the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by a person of ordinary skill in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.

In the following description, the use of PWM to control SMA actuators is described as a representative example.

(first embodiment)

First, the operation principle of the present embodiment will be described with reference to fig. 1 to 4.

Fig. 1 is a schematic diagram of electrical connections of SMA-OIS. As shown in fig. 1, the controller 204 for controlling OIS and OIS actuator 202 are connected by wires. Each of the shape memory alloy (shape memory alloy, SMA)

wires

102a, 102b, 102c, and 102d is connected to one of the

PWM sources

206a, 206b, 206c, and 206d through one of the amplifiers 210 for driving.

For heating the wire, current may be applied to the SMA wire through a corresponding one of the

PWM sources

206a, 206b, 206c, and 206d. Its current should be controlled by PWM method to reduce its huge power consumption. In addition, a temperature sensor 208 is used in the system to measure the temperature of each wire to improve its control accuracy. A structure including the temperature sensor 208 and the plurality of SMA wires 120 driven by the time-sharing drive (fig. 2 and 3) is employed to reduce the size of the camera module.

The

PWM sources

206a, 206b, 206c, and 206d generate PWM signals based on the temperature of the connected SMA wires measured by the temperature sensor 208. It is contemplated that this system implementing a miniature camera module can control the position of the movable unit 110 because each of the

SMA wires

102a, 102b, 102c, and 102d can shrink in length by heating.

Fig. 2 shows a configuration of time-division driving. In FIG. 2, SMA WIRE 304 includes four SMA WIREs WIRE0, WIRE1, WIRE2, and WIRE3. Filaments WIRE0, WIRE1, WIRE2 and WIRE3 have resistance values r0, r1, r2 and r3, respectively. One end of WIREs WIRE0, WIRE1, WIRE2 and WIRE3 is connected to analog-to-digital converter (ADC) 302 and temperature sensor 308. If the SMA wire is considered to have a resistance with a temperature characteristic, the temperature may be estimated from the output voltage by determining the divided voltage output of the SMA wire and the resistance for measurement included in the temperature sensor 308. The output voltage is converted to a digital value by ADC 302.

The other end of SMA WIRE0 is connected to a transistor 306a, the gate of which transistor 306a is connected to PWM source 206a which outputs PWM signal PWM 0. The other end of SMA WIRE1 is connected to a transistor 306b, the gate of which transistor 306b is connected to PWM source 206b which outputs PWM signal PWM 1. The other end of SMA WIRE2 is connected to a transistor 306c, the gate of which transistor 306c is connected to PWM source 206c which outputs PWM signal PWM 2. The other end of SMA wire3 is connected to a transistor 306d, the gate of which transistor 306d is connected to PWM source 206d which outputs PWM signal PWM 3. When the PWM signal of the gate input by the transistor is turned on, a current flows. By turning on/off the transistors 306a to 306d using the PWM sources 206a to 206d, current from the transistors 306a to 306d is supplied to the SMA wire 304.

Fig. 3 shows the time variation of the PWM signals used to drive SMA WIREs WIRE0, WIRE1, WIRE2, and WIRE3. As shown in FIG. 3, the temperature of each of the SMA WIREs WIRE0, WIRE1, WIRE2, and WIRE3 should be calculated from the ADC input voltage, which is proportional to the measurement of each SMA WIRE. By heating the SMA wire 304 with electricity, a fastening force is generated, and this fastening force is used as a lens driving force to drive the lens. Here, the lengths of one period (PWM carrier period) of the four PWM signals are the same. Further, the four PWM signals change to the high level state at different times. Furthermore, the four PWM signals may have different duty cycles. Such an approach generally has the advantage of being easy to reduce the size and weight of the electronic device, and can obtain relatively large forces.

Next, noise generated in analog-digital (AD) conversion used in image sensors such as a CCD and CMOS image sensor of a camera will be described. Among such noises, kTC noise, vth shift, and 1/f noise are well known. To counteract several types of noise, correlated double sampling (correlated double sampling, CDS) is typically implemented on ADCs in image sensors. In the CDS operation, double sampling is performed on a reset level (reset sampling) and a signal level (signal sampling), and an output signal is defined as a differential value of the reset sampling and the signal sampling. This operation can eliminate noise that is typically contained between the reset sample and the signal sample. The frequency response of the CDS is defined as the time interval T between two samples, as follows:

fig. 4 is a bode plot of CDS as a filter according to the above formula. In the figure, the vertical axis represents the gain (dB) of the frequency response, and the horizontal axis represents the frequency (1/T). The solid line is drawn according to the CDS transfer function. These lines are approximated by dashed lines. As shown in fig. 4, the CDS has a transmission characteristic of a band pass filter. Specifically, it acts as a high pass filter in the frequency range below 1/2T and completely cancels out the frequency components of n/T.

Next, with reference to fig. 5 and 6, CDS implemented in the COMS image sensor will be described. Fig. 5 shows a configuration of a CMOS image sensor in which ADCs of pixel columns perform CDS. The CMOS image sensor 600 includes a row decoder and driver 608, a pixel array 602, a comparator 604, a counter 605, a buffer 606, a RAMP generator 610, and a counter clock 612. The pixel array 602 includes a plurality of pixels. The pixel has a photodiode and a floating diffusion (floating diffusion, FD), and the FD stores charge obtained by the photodiode. A row of pixels specified by signals from the decoder and driver 608 is driven. The voltage from the pixel output of the pixel array 602 is compared with the voltage of the RAMP signal from the RAMP generator 610 in the comparator 604, and the time when the comparator output changes is output to the buffer 606 by the counter 605.

Here, the RAMP signal is a control signal for analog-to-digital converting an image captured by the image sensor. The counter 605 counts the number of pulses from the counter clock 612. Specifically, the counter 605 adds or subtracts the counted number of pulses to or from the counter value according to the output value from the comparator 604. The output of the comparator 604 is in a low state when the voltage of the RAMP signal is higher than the voltage of the pixel output, and the output of the comparator 604 is in a high state when the voltage of the RAMP signal is lower than the voltage of the pixel output. In the example shown in fig. 5, when the output of the comparator 604 rises in the buffer 606, the pixel value is replaced with a digital value by storing the counter value of the counter 605.

Fig. 6 is a signal diagram in CDS implemented on a COMS image sensor. In fig. 6, the upper solid line shows a RAMP signal as a reference for AD conversion, and the broken line shows a pixel output (analog input) voltage. The lower solid line shows the output of comparator 604. The first slope of the RAMP signal starts at time t 0. The reset operation is performed during the reset level from time t0, and the counter 605 performs the countdown operation. Next, when the output level of the comparator 604 rises, counting is stopped at time t1, and a counter value is stored in the buffer 606. Then, the second slope starts from time t 2. The signal output operation is performed during the signal level period from time t2, and the counter 605 starts counting up. Next, when the output level from the comparator 604 rises, counting is stopped at time t3, and a counter value is stored in the buffer 606. Then, the digital value of the pixel output is obtained by calculating the difference between the two counter values stored in the buffer 606 and obtaining the difference between the digital values. In this way, CDS is performed, and noise components contained in pixel outputs can be removed.

In fig. 6, the pixel output may fluctuate as indicated by arrow 502 due to noise derived from the PWM signal for OIS driving. Due to such fluctuation, the comparison result of the comparator 604 fluctuates, and the rise time of the output signal also fluctuates within the range indicated by the

arrows

504 and 506. The fluctuation of the rise time of the comparator 604 further causes fluctuation of the CDS time interval, thereby causing noise.

Next, with reference to fig. 7 and 8, the limitation of PWM control when CDS is performed will be described.

Fig. 7 shows a configuration example of the lens actuator system. The lens actuator system 800 includes a lens unit 808 and a servo controller 814. The lens unit 808 includes a lens 804, an actuator 806, and a gyro sensor 812. The servo controller 814 includes a driver 810, a PWM signal generator 820, and a duty cycle generator 816. In this configuration, when an image is captured using the lens actuator system 800, the image is input from the lens 804 to the imaging unit 802. The imaging unit 802 includes an image sensor, and the image sensor outputs an image signal DATA based on an analog signal from the lens 804. The imaging unit 802 also outputs the control signal Sctrl to the PWM signal generator 820.

Information about the movement of the lens 804 is obtained by a gyro sensor 812. The gyro sensor 812 outputs the SENS _ OUT signal to the duty cycle generator 816.SENS _ OUT is the lens movement information (acceleration, speed and position of the lens). The duty cycle generator 816 calculates the duty cycle of the PWM signal to be generated based on the sens_out signal. The calculated duty cycle is sent to the PWM signal generator 820. The PWM signal generator 820 generates a PWM signal Sdrv0 based on the input duty ratio and the control signal Sctrl, and transmits the generated PWM signal Sdrv0 to the driver 810. The driver 810 generates a driving signal Sdrv based on the PWM signal Sdrv0 and outputs it to the actuator 806. The actuator 806 moves the lens 804 based on the driving signal Sdrv to perform OIS control.

Fig. 8 shows waveform diagrams of signals for performing CDS in an ADC and PWM signals for OIS driving. In fig. 8, the top solid line represents a RAMP signal, and the broken line represents a pixel output (analog input). The second row shows the output of the comparator. The third row shows the control signal Sctrl. The fourth signal to the sixth signal represent PWM signals having duty ratios of 10%, 40% and 90%, respectively. When CDS is performed in the ADC, if the PWM signal level is different at rising times t1 and t2 of the comparator output, noise may be caused. Therefore, when the drive control is performed with a plurality of PWM signals, the plurality of PWM signals preferably have the same level at the rising times t1 and t2 of the comparator output during the AD conversion operation period t 0.

For four SMA wires driven with time division, it may be difficult to implement this technique because its maximum pulse width and PWM signal frequency are constrained by the AD conversion period.

The present invention provides a method of avoiding interference noise generated by a PWM driver without setting a frequency limitation between an AD conversion operation and the PWM driver.

In this embodiment, the waveform modulator generates an output signal to an actuator or other device by modulating the output PWM signal to drive the devices according to the following rules:

(1) The output PWM signal (H/L) is not switched during the switching prohibition period defined by the MASK signal.

(2) Outside the switching prohibition period, (a) the output PWM signal is set so that its duty ratio is the same as that of the reference PWM signal, or (b) if the output duty ratio is equal to that of the reference PWM signal, the output PWM signal is set as the reference PWM signal. Here, the switching prohibition period should include a CDS period (i.e., CDS period) between the start of the reset sampling and the end of the signal sampling.

According to this embodiment, the waveform modulator includes a duty cycle error monitor that measures the length of time that the output H/L state period differs from the H/L state period of the reference PWM signal. The waveform modulator then generates an actual PWM signal by modulating the reference PWM signal based on the output of the duty cycle error monitor and the MASK signal. Here, the MASK signal indicates a prohibition period for prohibiting switching of the output PWM signal (H/L).

Fig. 9 is a block diagram of a lens actuator system with a waveform modulator provided by the present embodiment. The definition of each signal shown in fig. 9 is as follows.

MASK is a control signal defining the inhibit period to be switched. SENS _ OUT is the lens movement information (acceleration, speed and position of the lens). Ref_pwm is a reference PWM signal whose duty cycle is determined by the servo system. ERR is a flag signal indicating that the actual duty cycle is higher/lower than the target duty cycle. Further, act_pwm is a pulse train of an actual PWM signal for the moving actuator.

The lens actuator system 900 includes a lens unit 902, a servo controller (PWM driver) 904, and an image sensor with CDS 906. The lens unit 902 includes a lens 908, an actuator 910, and a gyro sensor 912. The servo controller (PWM driver) 904 includes a driver 914, a waveform generator 919, and a PWM signal generator 920. The waveform generator 919 includes a waveform modulator 916 and a duty cycle error monitor 918. In this configuration, when capturing an image using a camera comprising the lens actuator system 900, pixel outputs are input from the lens 908 to an image sensor having the CDS 906. The image sensor having the CDS906 is used to perform a conversion process of converting an analog signal of a captured image into a digital output. The image sensor having CDS906 performs CDS in AD conversion for pixel output (analog input) from the lens 908, and outputs an image signal DATA. Further, the image sensor having the CDS906 outputs MASK signals to the waveform modulator 916.

Information about the movement of the lens 908 is output to the gyro sensor 912. The gyro sensor 912 outputs a sens_out signal to the PWM signal generator 920 based on the received movement information of the lens 908. The PWM signal generator 920 generates a ref_pwm signal based on the sens_out signal and outputs it to the waveform modulator 916 and the duty cycle error monitor 918. The duty cycle error monitor 918 counts the number of pulses of a clock for controlling the imaging unit. In addition, the duty cycle error monitor 918 generates an ERR flag based on the ref_pwm signal and the act_pwm signal from the waveform modulator 916, and outputs the ERR flag to the waveform modulator 916. The waveform modulator 916 generates the ACT_PWM signal based on the MASK signal, the REF_PWM signal, and the value of the ERR flag. The actpwm signal is output to the driver 914 and the duty cycle error monitor 918. The driver 914 outputs an input actpwm signal to the actuator 910. The actuator 910 drives the lens 908 based on the actpwm signal.

Fig. 10 is a waveform diagram for explaining a waveform operation of the waveform modulator. In fig. 10, the first line is a RAMP signal for AD conversion. The second signal represents MASK and the third signal represents ref_pwm. The fourth signal shows the counter value of the counter included in the duty cycle error monitor 918 and the fifth signal shows the value of the ERR flag. In addition, the last signal shows the actpwm signal.

The MASK signal indicates a disable period of the H state. During the inhibit period, act_pwm is controlled so as not to be switched. The prohibition period is set to include a period from the start of the reset operation to the end of the signal output operation in one period of the AD conversion.

The duty cycle of ref_pwm is set based on sens_out from the gyro sensor 912. In the present embodiment, the duty ratio is set to 60%.

Referring to the counter value CNT, when the reference PWM signal ref_pwm is L and the waveform modulator 916 outputs H, the duty cycle error monitor 918 counts up as indicated by arrows 1002 (t 1 to t 2). When the reference PWM signal ref_pwm is H and the waveform modulator 916 outputs L, the duty cycle error monitor 918 counts down as indicated by arrows 1004 (t 3 to t 4) and 1006 (t 5 to t 7). The ERR flag is set to-1 when the counter value is positive and set to 1 when the counter value is negative. Therefore, when the counter value CNT is positive (err= -1), the H-level period of the output signal act_pwm is shorter than that of the reference PWM signal ref_pwm. On the other hand, when the counter value CNT is negative (err= +1), the L-level period of the output signal is smaller than that of the reference PWM signal ref_pwm. The waveform modulator 916 selects an output level with reference to the counter value.

The ACT_PWM signal is in the L state when the ERR flag is-1 (t 3), and in the H state when the ERR flag is +1 (t 7). Therefore, the act_pwm signal is set as follows:

(1) When CNT is positive, ACT_PWM is L

(2) When CNT is negative, ACT_PWM is H

(3) When CNT is "0", the output signal is the same as the reference PWM signal REF_PWM

According to the above operation, the switching prohibition period is set so that the actual PWM signal is not switched during the AD conversion process of converting the analog signal of the image captured by the image sensor into the digital output. Accordingly, the PWM state changes within one period of CDS, and noise in AD conversion of the image sensor is suppressed.

Fig. 11 shows a relationship between the RAMP signal and the actpwm signal for the AD conversion operation in the period (X) of fig. 10. In fig. 11, the output level of the act_pwm remains unchanged during one cycle of the AD conversion operation. Further, as indicated by

arrows

1102 and 1104, the average duty cycle is the same as the duty cycle of ref_pwm. Thus, the waveform modulator 916 may switch the actual PWM signal such that the actual PWM signal approximates the duty cycle of the reference PWM signal.

Fig. 12 is a state transition diagram of the present embodiment. In fig. 12, there are six

states

1301, 1302, 1303, 1304, 1305, and 1306. In the three

states

1301, 1302, and 1303 on the left side, act_pwm is in the H state. Further, in the three

states

1304, 1305, and 1306 on the right side, act_pwm is in the L state. In addition, CNT for both

central states

1302 and 1305 are 0. The upper two

states

1301 and 1304 have positive CNTs and the lower two

states

1303 and 1306 have positive CNTs. In addition, in the case of the optical fiber,

indicating that the conditions are determined regardless of the value of MASK.

For example, in state 1302, ACT_PWM is in the H state and CNT is 0. If ref_pwm=h, the state is unchanged. Here, when ref_pwm becomes L, the state 1301 is shifted if mask=h, and the state 1305 is shifted if mask=l. In state 1301, if after CNT decrements, ref_pwm=h, mask=l, and CNT >0, then transition to state 1304. If ref_pwm=l, mask=l, then state 1304 is also transitioned. On the other hand, if after CNT is reduced, ref_pwm=h, mask=l, and cnt=0, then transition to state 1305 is made.

According to the present embodiment, when the MASK signal is set to high (H), the act_pwm is not switched. Here, "high" refers to a period of AD conversion using CDS, which is a period from the start of a reset operation to the end of a signal output operation in one period of AD conversion. This means that the ripple of the PWM signal edge does not cause noise during the AD conversion. Therefore, the AD conversion operation does not appear noise due to the switching of the act_pwm. Therefore, there is no need to consider the limitation of the relationship between the PWM carrier frequency and the AD conversion period.

(second embodiment)

In a preferred embodiment according to the present invention, the counter in the duty cycle error monitor 918 may have the ability to count the number of clocks of the duty cycle control clock of the PWM signal for a period twice as long as the switching prohibition period. That is, if the number of pulses in one switching prohibition period is T (the "count number" in fig. 13), the value from-T to +t should be stored in the counter.

When a counter may overflow, in one embodiment, waveform modulator 916 may be used to switch its output in the event of a counter overflow in the duty cycle error monitor to account for data overflow. In this case, the count number CNT can be switched even in the switching prohibition period. In this case, even in one prohibition period, the actual PWM signal can be switched. However, in general, the down-count of the reset operation starts from the first half of one AD conversion period, and the up-count of the signal output operation starts from the second half of one AD conversion period. On the other hand, switching due to count-down overflow may occur in the latter half of the inhibit period. Thus, by controlling the switching as described above, the influence of overflow of the counter value for monitoring the duty cycle error can be reduced.

Fig. 13 is a schematic diagram showing an operation waveform in the case where the duty ratio error monitor 916 provided in the present embodiment overflows. In fig. 13, the range of the countable numbers of the counter value CNT is indicated by an arrow 1406. On the other hand, the range of actual values is set to be narrow, as indicated by arrow 1408. The CNT up-count starts at time t 0. Since CNT overflows at time t1, act_pwm changes from the L state to the H state even during the prohibition period, as indicated by an arrow 1404. When CNT does not overflow, act_pwm becomes H state at time t 2. Even in the prohibition period, generally, when the comparator responds to a large signal input level, the time t1 thereof is located in the latter half of the AD conversion period. In the case of a large signal input level, the influence of noise on the image signal becomes relatively small.

Fig. 14 is a state transition diagram of the present embodiment. Unlike fig. 12, when CNT reaches a maximum value (cnt=max) in state 1301, the state transitions to state 1304, as indicated by arrow 1502. Further, when CNT reaches a minimum value (cnt=min) in state 1306, the state moves to state 1303, as indicated by arrow 1504.

According to the present embodiment, PWM control can be continued with less noise while reducing the influence of counter overflow.

(third embodiment)

Fig. 15 is a block diagram of a lens actuator system with a waveform modulator provided in a third embodiment of the invention. The lens actuator system 1600 has substantially the same configuration as that shown in fig. 9, except that the waveform generator 919 includes a MASK generator 1602. The MASK generator 1602 generates a MASK signal based on a horizontal synchronization signal HSYNC output from the image sensor having the CDS 906. Since the horizontal synchronization signal HSYNC is a synchronization signal for AD conversion, a MASK signal can be generated in synchronization with the AD conversion process. The effects of the present invention can be obtained even when a MASK signal is generated by the servo controller (PWM driver) 904.

Fig. 16 shows a signal waveform diagram when the lens actuator system 1600 provided in the present embodiment is applied to drive four SMA. The PWM signals act_pwm for driving the four WIREs, i.e., WIREs WIRE0, WIRE1, WIRE2, and WIRE3, are switched outside of the inhibit period. The reference PWM signal ref_pwm and the actual PWM signal act_pwm on each wire are compared, and the duty cycles of the two PWM signals are similar.

As described above, according to the present invention, the PWM signal is modulated by (1) a MASK signal that modulates the PWM signal to prohibit switching during one cycle of the AD conversion operation, and (2) a measurement result of a duty error caused by non-switching. The reference PWM signal is switched to match its duty cycle to a target duty cycle of the servo loop based on the error in the duty cycle to account for the switching prohibition period defined by the MASK signal.

Therefore, the influence of noise on the pixel output AD conversion can be eliminated without being limited by the combination of the PWM carrier frequency and the AD conversion period.

In addition, by monitoring the communication channel between the imaging sensor and the lens driver, and modulating PWM signals for driving the actuator, etc., noise can be easily eliminated.

The present invention is applicable to a system having ADCs embedded in various sensors and PWM actuators (e.g., image sensors and lens actuators driven by stepper motors, etc.) near the sensors to reduce the effect of exhaust noise due to actuator driving.

The summary is merely a specific implementation of the invention and is not intended to limit the scope of the invention. Any changes or substitutions that would be apparent to one of ordinary skill in the art within the scope of the present disclosure are intended to be within the scope of the present invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.

Claims

1. A PWM driver for generating a PWM signal for driving a lens, comprising:

2. The PWM driver of claim 1, wherein the PWM signal generator generates the reference PWM signal based on movement of the lens.

3. The PWM driver according to claim 2, wherein the generator obtains movement information from a gyroscopic sensor that detects the movement of the lens.

4. A PWM driver according to any one of claims 1 to 3, wherein the switching inhibit period is set based on a control signal for analog-to-digital conversion of an image captured by the image sensor.

5. A PWM driver according to any one of claims 1 to 4, further comprising a counter for increasing or decreasing a counter value of a pulse number of a clock according to an H-state or an L-state of the actual PWM signal, wherein the modulation unit is configured to switch the actual PWM signal based on the counter value to minimize an absolute value of the counter value outside the switching prohibition period.

6. The PWM driver according to claim 5, wherein the range of the counter corresponds to a period of the reference signal of the analog-to-digital conversion.

7. The PWM driver according to claim 6, wherein the modulation unit switches the actual PWM signal when the counter value overflows during the switching prohibition period.

8. The PWM driver according to any one of claims 1 to 7, wherein the mask signal is generated based on a control signal for analog-to-digital converting an image captured by the image sensor.

9. A PWM driver according to any one of claims 1 to 8, wherein the switching inhibit period is set such that the actual PWM signal does not switch during the conversion process of converting an analog signal of an image captured by an image sensor into a digital output.

10. The PWM driver according to any of claims 1 to 9, further comprising a monitor for instructing the modulation unit to switch the actual PWM signal based on the reference PWM signal and the actual PWM signal.

11. The PWM driver according to claim 10, wherein the monitor instructs the modulation unit to switch the actual PWM signal such that the actual PWM signal approximates the duty cycle of the reference PWM signal.

12. The PWM driver according to any one of claims 1 to 11, further comprising a mask generating unit for generating the mask signal.

13. An actuator system, comprising:

a PWM driver according to any one of claims 1 to 12;

14. A camera module, comprising:

the actuator system of claim 13;

15. A method for generating a PWM signal for driving a lens, comprising:

generating a reference PWM signal switched at a predetermined period;

receiving a mask signal defining a switching prohibition period;

16. The method of claim 15, wherein the step of generating the reference PWM signal generates the reference PWM signal based on movement of the lens.

17. The method of claim 15 or 16, wherein the step of generating the reference PWM signal obtains movement information from a gyro sensor that detects movement of the lens.

18. The method according to any one of claims 15 to 17, wherein the switching prohibition period is set based on a control signal for analog-to-digital converting an image captured by an image sensor.

19. The method according to any one of claims 15 to 18, further comprising:

20. The method of claim 19, wherein the range of the counter corresponds to a period of the reference signal of the analog-to-digital conversion.

21. The method of claim 20, wherein the step of generating the actual PWM signal switches the actual PWM signal when the counter value overflows during the switch-inhibit period.

22. The method of any one of claims 15 to 21, wherein the mask signal is generated based on a control signal for analog-to-digital converting an image captured by an image sensor.

23. The method of claim 22, wherein the switching prohibition period is set such that the actual PWM signal is not switched during a conversion process of converting an analog signal of an image captured by an image sensor into a digital output.

24. The method according to any one of claims 15 to 23, wherein the step of generating the actual PWM signal comprises switching the actual PWM signal based on the reference PWM signal and the actual PWM signal.

25. The method of claim 24, wherein the step of generating the actual PWM signal switches the actual PWM signal such that the actual PWM signal approximates the duty cycle of the reference PWM signal.

26. The method according to any one of claims 15 to 25, further comprising the step of generating the mask signal.